Researchers at Oregon State University have developed a fast-setting, environmentally friendly alternative to concrete that they hope can one day be used for rapid 3D printing of homes and infrastructure.
3D printing, also known as additive manufacturing, is already being used to solve challenges in construction, such as the global housing crisis, which is looming at a time when the world's population is approaching 8.5 billion.
But cement, the binding agent in concrete, is responsible for about 8% of global carbon dioxide emissions, and concrete's curing time – which can be several days – as well as required structural supports can hinder the progress of construction projects.
The new clay-based material, developed by Devin Roach, Nicolas Gonsalves and collaborators at Oregon State, hardens as it is extruded from the printer thanks to its acrylamide-based binder, which undergoes a chemical reaction known as frontal polymerization. The material can even be printed over unsupported gaps, such as the top of a door or window opening.
“The printed material has a buildable strength of 3 megapascals immediately after printing, allowing the construction of multi-layer walls and free-standing overhangs such as roofs,” said Roach, an assistant professor of mechanical engineering in the OSU College of Engineering. “It exceeds 17 megapascals, the strength required for residential concrete, in just three days, compared to up to 28 days for traditional cement-based concrete.”
And because the new material is mostly made of soil enriched with hemp fiber, sand and biochar — carbon-rich material created by heating wood chips and other organic biomass under low oxygen levels — its environmental footprint is much smaller than that of concrete. Concrete's binding agent, cement, is produced through carbon-releasing reactions in industrial furnaces heated to over 1,400 degrees Celsius, typically by energy produced by burning fossil fuels.
“I am incredibly proud of our innovative, transdisciplinary team that has developed a material that can change people’s lives in many ways,” said Roach. “Especially given the frequency of destructive natural disasters, we need to be able to build shelters and other structures quickly – using materials that are readily available and have relatively low emissions.”
Gonsalves, a graduate student, led the research, which also included Ashlei Morgan, Heidi Thiele, Andre Olarra and Adam Bischoff from the School of Mechanical, Industrial and Manufacturing Engineering; Pavan Akula from the Faculty of Civil and Civil Engineering; Islam Hafez from the College of Forestry; and Yakun Zhang of the College of Agricultural Sciences.
The study, published in Advanced Composites and Hybrid Materials, was supported by the U.S. Department of Agriculture, OSU's Global Hemp Innovation Center and the College of Engineering.
“Currently our material costs more than traditional cement-based concrete, so we need to lower the price,” Roach said. “Before it can be used, we must also follow the American Society for Testing and Materials’ standard tests and prepare a report for professional engineers to review and approve when its use in construction projects is proposed.”
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